The AK09973D is  a 3-axis magnetic sensor IC, that utilizes Hall sensor technology.

The AK09973D is equipped with a wide-range magnetic sensor that detects a large magnetic field, a sensor driver, a signal amplifier, a calculation logic, etc., and outputs the magnitude of the magnetic field in each of X,Y,Z axes as digital value. In addition, it has a switch function to detect magnetic events according to the threshold setting and notify the outside.
The AK09973D is suitable for use in combination with magnets to detect the relative distance and orientation of the two. 
It is ideal for detecting the shape of foldable and screen-rollable smartphones, and fir ultra-low consumption security applications that utilize the switch function.